The NICHD's Contraceptive Clinical Trials network conducts Phase I, II and III clinical trials of a wide variety of new female and male contraceptive methods. The objective of this contract is for CCTN contractors to conduct female contraceptive clinical trials, conduct treatment trials of gynecologic conditions, and to develop research protocols on a task Order basis under an Indefinite Delivery/Indefinite Quantity (IDIQ) contract. There is a demand for new methods of contraception that can provide effective protection against unintended pregnancy as well as reduce the risk of venous thromboembolism (VTE), particularly for obese women. A new vaginal ring that can deliver a high dose progestin (Nestorone) and a low dose of estradiol (E2) may provide effective and safe contraception for women. The objective of the dose finding study is to identify a dose that can provide reliable contraception and acceptable bleeding patterns for up to 6 months of useThe proposed study will evaluate contraceptive efficacy , pharmacokinetics, bleeding patterns and safety and side effects of a Nestorone & estradiol ring for women.